'assail' originates from Old French, specifically the word 'assaillir', where 'as-' meant 'toward' and 'sallir' meant 'to leap'.

'assaillir' transformed into the Middle English word 'assailen', and eventually became the modern English word 'assail'.

Initially, it meant 'to leap upon or attack', but over time it evolved into its current meaning of 'to attack vigorously'.